It is known that due to their predominantly hydrophobic molecular structure, fatty acid-modified alkyd resins are insoluble in water and can be used as coating materials only when dissolved in organic solvents. For the development of environmentally acceptable lacquer systems, many attempts have been made in past years to modify lacquer binders to become emulsifiable in water, dilutable with water, or soluble in water. To achieve this, the hydrophobic alkyd resin must then be made sufficiently hydrophilic that it can be applied from an aqueous medium while, at the same time, the hydrophobic nature of the alkyd resin residue furnishes a lacquer coating that is as water-resistant as possible.
A known method for hydrophilation is the introduction of numerous carboxyl groups into alkyd resins, which polycarboxyl alkyd resins can then become water-soluble as amine salts. However, such anionically hydrophilized lacquer systems do not constitute a satisfactory solution to the problem of providing suitable binders because they contain relatively large quantities of volatile amines and, often, auxiliary organic solvents. In addition, due to the anionic nature of the binder, the lacquer film is sensitive to water and, in particular, to alkaline media.
Furthermore, it would be expected that use of aqueous emulsions or dispersions of alkyd resins would make a more favorable solution of the problem possible. Organic solvents would, for the most part, be unnecessary, and the component of volatile amines could be kept small. However, the stabilization of such emulsions is primarily achieved by condensing polyethylene glycol chains. The polyethylene glycol chains are disadvantageous because, on the one hand, the resulting lacquer coatings lack stability to water since the hydrophilic chains remain unchanged in the lacquer film, and because, on the other hand, the emulsions are characterized by typical lack of stability and insufficient degree of dispersion. Thus, there has been no major practical use of such alkyd resin emulsions.
Applicants have surprisingly found that the described disadvantages can be overcome. They have found that alkyd resins particular fatty acid modified alkyd resins can be prepared that, on the one hand, are easily dispersible in water or will form a practically clear solution without requiring major amounts of amines and that, on the other hand, keep the sensitivity of the hardened lacquer films to water as low as possible.